This invention relates to small low-cost battery chargers offering superior charging performance for consumer-size rechargeable batteries and more versatility over known chargers.
The present invention is an improvement over existing battery charging systems of the type described in U.S. Pat. No. 4,009,429. Such a charging system is marketed by General Electric Company, and enables cells of several different sizes to be charged. It comprises a battery charger unit which can be plugged into an electrical receptacle and one of several mating cell-holding modules which holds and interconnects two or four rechargeable cells.
The foregoing battery-charging system has achieved wide commercial acceptance with the public. It is effective, relatively inexpensive and easy to use. The terminals on the battery charger unit, and the construction of the cell-holding modules are such that it is virtually impossible to incorrectly mate the cell holding module with the battery charger. An important feature of that charger is the fact that it can be plugged directly into an electrical receptacle so that the charger, when mated with the cell-holding module, forms an integral unit that is supported by the receptacle itself. This eliminates the need for electric extension cords and the like, and enables the consumer to leave the charger plugged into the receptacle during cell charging. Moreover, the charger current is such that the cells may be left on "on-charge" continuously.
A limiting feature of the existing battery charger just described, however, is the fact that it can accept only one type of cell-holding module at any given time. Thus, should it be desired to charge immediately a pair of needed C-size cells while AA-size cells, for example, are being charged, the AA cell-holding module must be removed from the charger before charging is complete in order to substitute the C-size cell module. Another limitation of the existing charger is the fact that its charging current is restricted to about 0.1C, where C is the capacity of the cell in ampere-hours (Ah). Thus, for a typical AA-size battery having a nominal open circuit voltage of 1.2 volts and a capacity of 0.5 Ah, the C/10 charge current rate is 50 mA. At this rate, the recommended charging time is 12-16 hours. It is desirable to increase the charging rate up to about C/6 or 0.15C in order to enable the cells to attain full charge in 8-12 hours.
In order to achieve a higher charge rate, however, a larger transformer is required. This, in general, requires that the battery charging unit be able to withstand the greater mechanical loads transmitted to the blade connectors which plug into the outlet receptacle.
The present invention carries forward the teachings and advantages of the battery chargers and charging systems described in the above-mentioned U.S. Pat. No. 4,009,429. The present battery charger is adapted to mate with existing cell-holding modules but, in addition, supplies a greater charging current and is configured to accept two cell-holding modules simultaneously, whether the cells to be charged are the same or different sizes. Thus, in the present invention, it is possible to charge simultaneously cells of the AA, C and D size, as well as 9-volt application batteries. Additionally, the battery charger is arranged so that, when cell-holding modules are mated with it, the system does not block the second receptacle of a duplex outlet.